An inline concentration measurement device to be incorporated in a raw material fluid supply line of a semiconductor manufacturing equipment is conventionally known (for example, Patent Document 1).
FIG. 8 is a schematic diagram showing a configuration of an embodiment of a related concentration measurement device. In FIG. 8, light having a prescribed wavelength emitted from a light source 1 including a light emitting diode is transmitted to a light incident part 3 through an optical fiber 2, then entered to a gas flow path 5 through a window member 4 made of quartz glass, sapphire glass or the like equipped in the light incident part 3 to be absorbed by gas in the gas flow path 5, and finally received by a light receiving part 8 including a photo diode 7 through an opposing window member 6. The photo diode 7 converts the detected light into an electrical signal and outputs, then the outputted signal is sent to a control computation unit 10 including a CPU through an electric wiring 9, and gas concentration is finally displayed on a displaying part 11 after a certain computing process by the control computation unit 10 is conducted. The control computation unit 10 also controls a power source 12 for supplying power to the light source 1. The light source 1 is capable of emitting the light having one wavelength or two wavelengths or more.
As shown in a detailed cross section view of FIG. 9, the gas flow path 5 shown in FIG. 8 includes a metal measurement cell main body 15 with the gas flow path 5 formed, the light incident part 3 connected to the measurement cell main body 15 through a gasket 16, and the light receiving part 8 connected to the measurement cell main body 15 through a gasket 17. The gas flow path 5 includes a gas flow path part 5a for an optical path extending straight through between the light incident part 3 and the light receiving part 8 to provide an optical path L and a left-and-fight pair of communication parts 5b and 5c that communicate with the gas flow path part 5a for the optical path and open on a bottom face 15a of the measurement cell main body 15. The light incident part 3 is equipped with the window member 4 and the optical fiber 2. The light receiving part 8 is equipped with the window member 6 and the photo diode 7. A joint 20 at a gas inlet side and a joint 21 at a gas outlet side are connected to the bottom face 15a of the measurement cell main body 15.